ESTIMATION OF LOCAL ATTENUATION FROM MULTIPLE VIEWS USING COMPENSATED VIDEO SIGNALS

The effects of time gain control, nonlinear compression, beam diffraction, and nonuniform bandpass characteristic in an ultrasonic imaging instrument are compensated by video signal processing to calculate regional ultrasonic attenuation under a narrow-band assumption. Compensation for time gain control and amplitude compression is accomplished using a measurement of the digitized output value as a function of the time gain control. Compensation for beam diffraction is performed using the scattering from a random medium reference. Compensation for nonuniform bandpass characteristics employs a measurement of the relative amplitude response over the attenuation-induced frequency downshift experienced by the signal. The decay of the compensated signal envelope with range yields an attenuation value which is assigned to the nominal centre frequency of the instrument. The method is applied to calculate the attenuation in a model random medium using multiple views to obtain an attenuation of 4.0 +/- 0.5 dB/cm at 3.5 MHz in the relatively small region of 1.6 x 1.5 cm2. The calculations of attenuation value are within 5% of the value obtained using a radiation force balance system. The results indicate that video signal processing and multiple views can be used to quantify attenuation in regions of about 2 cm2 with an accuracy of the order of 10%.